valve characteristic control apparatus of internal combustion engine and methods of controlling valve characteristics

A camshaft (22) provided with three-dimensional cams (27) is connected at its one end to a valve lift-varying actuator (22a). By the valve lift-varying actuator (22a) displacing the camshaft (22) in the directions of an axis of the camshaft (22), the lift characteristic of intake valves (20) set by the three-dimensional cams (27) is variably controlled to a target amount of valve lift. The valve lift characteristic related to this control is detected as a detected amount of valve lift by a reference-purposed detected portion and a cam angle sensor (126). An apparatus and a method diagnoses abnormalities in the valve lift-varying actuator (22a) by, for example, evaluating whether the amount of change in the detected amount of valve lift is at most a predetermined value and the absolute value of a difference between the detected amount of valve lift and the target amount of valve lift is greater than a predetermined value.